Modal analysis and tension estimation of stay cables using noncontact vision‐based motion magnification method

Abstract

Summary This paper describes a study on modal analysis and tension estimation of stay cables by vision‐based measurement under ambient condition. Microvibration of stay cable is captured by video camera, and the amplitude is amplified using phase‐based video motion magnification method. From the sequences of cable images, spatial displacements of the cable are extracted via discretized centroid searching method. Modal parameters of the cable, namely, natural frequency, damping ratio, and mode shape, are identified by dynamic mode decomposition method from cable displacement responses. Furthermore, tension of the stay cable is estimated based on the identified natural frequencies by minimizing an error function of an approximate relationship between frequency and tension iteratively. The technique is verified in the laboratory‐scale experiments and implemented to full‐scale measurement of medium size and long‐span cable‐stayed bridges. To compare the accuracy and efficacy of the vision‐based method, noncontact vibration measurement using laser Doppler vibrometer was also conducted. The results demonstrate that the proposed vision‐based vibration measurement techniques can estimate modal parameters and tension of the stay cables accurately in a noncontact and distant measurement under ambient condition. The proposed method offers an alternative of effective and accurate vibration measurement of stay cables using only motion of the cables recorded by video camera.

Estimating small structural motions based on sparsity enforcement

“…In this section, the sparsity‐enforcement method was used to evaluate the structural modal identification, and this includes the structural natural frequencies and damping ratios (Jana et al., 2022; Wangchuk et al., 2022). To calculate these results, at least two degrees of freedom of dynamics are required; therefore, like the qualitative comparisons of structural displacements, only the results in the y direction of Case 1 were used.…”

“…To offset these drawbacks, the phase-based method, as one type of target-free methods, established by complexvalued steerable pyramids, has been developed (Wadhwa et al, 2013). It has been applied in structural motion estimation (Yang et al, 2017;Shang & Shen, 2018), dynamic strain analysis (Yang et al, 2019), and modal identification (Jana et al, 2022;Wangchuk et al, 2022). The phase-based method is essentially one type of video magnification methods, which can be classified into Lagrangian and Eulerian methods.…”

A decoupled algorithm for cable parameter identification by frequency‐ratio‐offset

“…In recent work, Fujino et al. applied phase‐based video motion magnification (Wangchuk et al., 2022) and artificial neural networks (Le et al., 2022) to the stay cables of the Tatara Bridge. Jana et al.…”

Static and dynamic response analysis of stay cables using terrestrial laser scanning and vibration measurements

“…Frequencies and cable tensions have been identified through radar technique with the same accuracy of the ones obtained with conventional sensor measurements. Modal analysis and axial force identification of stay cables are also performed through visionbased measurement, with motion magnification methods used to amplify microvibration of stay cable captured by video camera [10]. If not based sufficiently refined mechanical methods, frequency-based approaches often neglect or underrate the effects of the chord inclination angle, cable extensibility, flexural stiffness, complex boundary conditions and cable-beam interactions.…”